The rubber and plastic industries have used and are still using extrusion apparatus with screw configurations consisting of helical extrusion grooves. The geometry of the helical groove exposes the process material, at the barrel and rotor extrusion groove surfaces, to high sheer and localized warming of the process material, which develops a flow pattern in the helical extrusion groove, consisting of a warmed outer layer of process material surrounding a cold core of process material. This formation requires downstream corrective action resulting in devices such as, various plow like devices, barrel to screw transfer as used in the Transfermix apparatus, pin-type obstructions in the rotor grooves and most often, increased length of the extruder, to develop the so called dwell time to allow the temperatures to equalize. This temperature stratification is more pronounced in the larger diameter extruders and has hindered the development of more economical large extrusion units.
Also, the extruders in use today, using helical groove rotors, have at their discharge ends the problem of changing from extrusion flow to plug flow, as required for extrusion uniformity. Extrusion flow, leaving the rotor end, is discharged in a circular path as a rotor turns, which causes a pulsing extrusion. Again corrective action must be provided. Special extrusion heads, with large volumn so as to provide dwell time to relax material flow lines, various type barriers arranged to rework the material flow lines, one or two roll extrusion dies, etc. are provided to process the extrusion material to the acceptable low stress plastic state.